Reinforced fabric

ABSTRACT

A fabric comprising elongated metal elements and thermoplastic material, said thermoplastic material being present in a volume of at least 40% of the total volume of said fabric, whereby at least part of the elongated metal elements are metal cords. The invention also relates to a method of manufacturing a reinforced article by applying heat and/or pressure to such a fabric.

FIELD OF THE INVENTION

[0001] The invention relates to a fabric comprising metal cords andthermoplastic material.

BACKGROUND OF THE INVENTION

[0002] Although a lot of efforts have been made to reinforce plastics,there is a considerable need for reinforced articles which combine thecharacteristics of having a high strength and a light weight.Furthermore, for certain applications it can be desirable that thereinforced polymer can be flexed or bent to shape.

[0003] Various means of reinforcing thermoplastic materials with metalhave been tried, including the use of metal rods or metal plates.WO99/10174 describes a thermoplastic article in the form of sheetmaterial, obtained by applying heat and pressure to a laminatecomprising an upper sheet of a copolyester material, metallic wire, rodsor bars and a lower sheet of a copolyester material.

SUMMARY OF THE INVENTION

[0004] It is an object of the present invention to provide a fabriccomprising elongated metal cords and a thermoplastic material. Thisfabric can be used to manufacture reinforced articles.

[0005] It is a further object to form metal reinforced articlescharacterised by a high strength to weight ratio.

[0006] It is also an object to reach a good adhesion between the metaland the thermoplastic material.

[0007] Furthermore it is an object to provide a method for themanufacturing of reinforced articles.

[0008] According to a first aspect of the present invention a fabriccomprising elongated metal elements and a thermoplastic material isprovided. At least part of the elongated metal elements are metal cords.

[0009] The thermoplastic material functions as filling element. Afterapplying heat and/or pressure to the fabric, the thermoplastic materialfills the interstices between the metal cords. This means that thethermoplastic material must be present in a sufficient volume to fillthese interstices. Therefore, the thermoplastic material is present in avolume of at least 40% of the total volume of the fabric. Morepreferably, the volume of the thermoplastic material is 50% of the totalvolume of the fabric. The total volume of the fabric has to beconsidered as the volume of the metal cords and the volume of thethermoplastic material out of which the fabric is made.

[0010] Any thermoplastic material can be considered as filling element.With a thermoplastic material is meant any thermoplast and anythermoplastic elastomer.

[0011] Examples of suitable thermoplastic materials are: polyethylene(PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate(PET), polyethylene napthalate (PEN), polybuteen terephthalate (PBT)polyvinylchloride (PVC), polyester, polyamide (PA), polyimide (PI),polycarbonate (PC), styrene acrilonitryl (SAN),acrylonitril-butadienestyrene (ABS), thermoplastic polyurethane (TPU),thermoplastic polyolefins (TPO), thermoplastic copolyetheresters,copolymers of these polymers or similar materials.

[0012] The polymer material can be present in the fabric as filaments.Alternatively, the thermoplastic material can be present as coating onthe metal cords or on a number of metal cords forming strips.

[0013] The total volume of the thermoplastic material present asfilament and/or as coating amounts to at least 40% of the total volumeof the fabric. In addition to the thermoplastic material present in thefabric, thermoplastic material can also be applied on the fabric.

[0014] Suitable filaments are for example polyamide filaments,polyethylene filaments, polypropylene filaments or polyester filaments.

[0015] For the purpose of this application, a filament has to beunderstood as an elongated element of a thermoplastic material. It mayhave various cross-sections, such as circular, oval, rectangular. Stripsmade from a thermoplastic material are also suitable.

[0016] Different filaments may be plied together to form filament yarn.

[0017] A fabric can be understood as a woven, knitted or braidedstructure.

[0018] Any metal can be used to provide the elongated metal elements.Preferably, alloys such as high carbon steel or stainless steel alloysare used.

[0019] At least part of the elongated metal elements are metal cords,such as steel cords.

[0020] Preference is given to steel cords with a large and rough surfaceso as to increase the mechanical anchoring in the matrix. Examples are3×3 or 7×3 cords.

[0021] Multistranded cords are preferred to single stranded cords.Suitable cords are high elongation cords and high impact cords.

[0022] In addition to the metal cords, metal wires can be present in thefabric. The wires may have various cross-sections and geometries, theymay for example be circular, oval or flat.

[0023] The tensile strength of the metal elements is preferably higherthan 1500 N/mm². The range of the tensile strength is for examplebetween 1500 N/mm² to 3000 N/mm² or even more.

[0024] It may be desired to use metal cords having a structuralelongation. Preferred metal cords have an elongation of more than 0.3%,for example 1%, compared to the initial length of the metal cord onwhich a force of at least 10% of the total force at rupture of theseelements is applied. The elongation of these metal cords is due to thestructural deformation of the metal cords.

[0025] The use of this type of metal cords features the advantage thatthe bending properties of the fabric are improved. When a fabriccomprising metal cords having a structural deformation is subjected to aforming process, the force needed to form the fabric into a shapedreinforced article is partially used to elongate the metal cord. Theforce applied will elongate the metal cord by partially removing thestructural deformation. A structural deformation can be an undulation,either uni- or multidirectional. Another deformation can be obtained byusing a metal cord having a spiral shape.

[0026] Different embodiments of a fabric according to the presentinvention can be considered.

[0027] A first group consists of fabrics comprising metal cords andpolymer filaments of a thermoplastic material.

[0028] The fabric may for example be a woven, braided or knittedstructure.

[0029] Some examples of woven structures are:

[0030] A fabric whereby metal cords form the warp, whereas the polymerfilaments form the weft or vice versa polymer filaments form the warpand metal cords form the weft.

[0031] A fabric whereby the warp and/or the weft are formed by acombination of metal cords and polymer filaments.

[0032] For example, the warp filaments comprise in turn a metal cord anda polymer filament.

[0033] The number of metal cords or polymer filaments of the warp andthe weft can be varied.

[0034] A second group of fabrics comprises fabrics made from metal cordscoated with a thermoplastic material.

[0035] The coating of a metal cord can be applied by any conventionalmeans. A possible coating method is extrusion.

[0036] For the purpose of the invention a coated metal cord has to beunderstood as an element substantially surrounded by at least one layerof a thermoplastic material.

[0037] This means that this can also be realised by wrappingthermoplastic threads or filaments around a metal cord.

[0038] It can be desirable that the metal cords are coated with a numberof consecutive layers of a thermoplastic material. The material mostclosely to the metal surface has an elastic modulus which approaches themodulus of the metal cord, whereas the outer layer of thermoplasticmaterial has a modulus approaching the modulus of the material in whichthe metal cord or cords is/are embedded. In the case, there are layersof a thermoplastic material present inbetween the most inner and themost outer layer, the modulus of these layers changes gradually. By thisconsecutive number of layers present around the metal cord, delaminationis avoided.

[0039] The fabric may be a woven, braided or knitted structure.

[0040] Examples of woven structures are:

[0041] A fabric whereby the warp and/or the weft are formed by coatedmetal cords.

[0042] Fabrics whereby the warp and/or the weft are a combination ofmetal cords and coated metal cords or a combination of polymer filamentsand coated metal cords.

[0043] A third group comprises fabrics made of strips.

[0044] A strip comprises two or more metal cords embedded in a matrix ofa thermoplastic material. The metal cords are preferably locatedparallel in the plane of the strip. A possible method of manufacturingsuch a strip is by coextrusion.

[0045] In addition to the thermoplastic material present in the fabric,thermoplastic material can also be applied on the fabric, either afabric of group one, two or three.

[0046] By varying the number of polymer filaments in the fabric, thediameter of the polymer filaments and/or the thickness of the coating,the total amount of the thermoplastic material can be influenced. Asdescribed above the total volume of the thermoplastic material presentin the fabric is at least 40% of the total volume of the fabric.

[0047] In the case of a woven fabric, the amount of thermoplasticmaterial can further be influenced by varying the weaving structure orthe inweaving factor, either of the warp or the weft or of both, or byvarying the number of filaments or metal cords per length unit of thefabric in warp or weft direction.

[0048] The inweaving factor is defined as the ratio of the length offilament to the length of the woven structure.

[0049] The fabrics may further comprise glass fibers, organic fiberssuch as carbon fibers and/or glass fibers or organic fibers coated witha thermoplastic material.

[0050] To improve the corrosion resistance of the metal cords, the metalcords can be coated with a metallic coating layer such as zinc or a zincalloy such as brass. Another suitable zinc alloy is an alloy comprising2 to 10% Al and 0.1 to 0.4% of a rare earth element such as La and/orCe.

[0051] In order to assure a good adhesion between the metal and thethermoplastic material, an adhesion promoter can be applied on the metalcord.

[0052] Possible adhesion promoters are bifunctional coupling agents suchas silane compounds. One functional group of these coupling agents isresponsible for the binding with the metal or metal oxides; the otherfunctional group reacts with the polymer.

[0053] More details about these coupling agents can be found in the PCTapplication WO-A-99/20682.

[0054] Other suitable adhesion promoters are aluminates, zirconates ortitanates.

[0055] The eventual use of a fabric according to the invention is tomanufacture reinforced articles.

[0056] In order to manufacture a reinforced sheet or a reinforcedarticle, a fabric comprising the metal cords and the thermoplasticmaterial is subjected to a temperature and/or pressure sufficient tocause the polymeric material to flow and fill the interstices betweenthe metal filaments. This can be done in one step or may requiresubsequent steps.

[0057] Alternatively, a layered structure, comprising a number offabrics according to the invention brought into contact with each other,is subjected to a heat and/or pressure treatment.

[0058] The fabric or layered structure is heated till a temperature thatallows the thermoplastic material to soften and to flow out. Thetemperature remains thereby lower than the melting point of the metalcords. The heat and/or pressure can for example be applied by feedingthe fabric through pressure rollers.

[0059] Since the metal cords have a high thermal and electricconductivity, the metal cords themselves can also be used to heat andsoften the thermoplastic material. The latter way of heating can beconsidered as very efficient since it decreases the time to soften thethermoplastic material.

[0060] After applying heat and/or pressure to the fabric or to thelayered structure, the thermoplastic material has preferably filled theinterstices between the metal cords and most preferably the metal cordsare completely embedded in the thermoplastic material.

[0061] During the manufacturing of a reinforced article, a fabricaccording to this invention has the advantage that it can be flexed orbent to shape. This can for example be realised by placing a fabric orpossibly a layered structure comprising a number of fabrics, in a press,possibly in a heated press.

[0062] Alternatively, a shaped reinforced article can be manufactured intwo successive steps. In a first step a reinforced sheet can be obtainedby applying heat and/or pressure to a fabric according to the inventionand in a second step, this reinforced sheet can be deformed to obtain areinforced article.

[0063] Possible forming processes are press forming, flow moulding,thermofolding and membrane forming.

[0064] In a press forming operation (stamping) a fabric or a reinforcedsheet is heated to processing temperature and stamped to shape in atwo-part-tool under pressure.

[0065] In a flow moulding operation (moulding) a fabric or a reinforcedsheet is heated to processing temperature, placed in a two-part-tool andthen under pressure the mould cavity is filled by polymer matrix flowinginto every recess of the mould.

[0066] In a thermofolding operation a fabric or a reinforced sheet isheated locally and folded.

[0067] In a membrane forming operation an autoclave pressure is used todrape the preheated fabric or reinforced sheet over a tool.

[0068] The reinforced article can further be embedded in a matrix ofthermoplastic material either before or after the forming process. Apossible method to realise this is by bringing the fabric into contactwith a thermoplastic sheet either at one side or at the upper side andat the lower side of the fabric. In this way a laminated structure isformed. The thermoplastic sheets are bonded to the fabric for example bypressing the laminated structure through heated rollers.

[0069] An alternative method to embed the fabric in a matrix of athermoplastic material is by overinjection or overextrusion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The invention will now be described into more detail withreference to the accompanying drawings wherein

[0071] FIGS. 1 to 5 shows different embodiments of fabrics comprisingmetal cords and filaments of a thermoplastic material;

[0072]FIG. 6 shows a coated metal cord;

[0073]FIG. 7 is an illustration of a woven fabric comprising coatedmetal cords;

[0074]FIG. 8 shows a strip, comprising a number of elongated metalmembers embedded in a matrix of a thermoplastic material.

[0075]FIG. 9 illustrates a woven fabric comprising strips.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0076] FIGS. 1 to 5 are illustrations of fabrics according to the firstgroup of fabrics, comprising metal cords and polymer filaments of athermoplastic material.

[0077]FIG. 1a shows a woven fabric 10. Metal cords 12 form the warp,whereas polymer filaments 14 such as polyamide filaments form the weft.The metal cords are for example steel cords of the type 7×7×0.15. Thetotal volume of the polymer amounts to 50% of the total volume of thefabric.

[0078]FIG. 1b shows the cross-section of a woven fabric 10.

[0079]FIGS. 2 and 3 shows two embodiments of woven fabrics 20 and 30,whereby the weft comprises steel cords 22 and 32, and the warp comprisespolyamide filaments 24 and 34.

[0080] The steel cords are of the type 7×3×0.15.

[0081] The number of polymer filaments can be increased in order toincrease the total amount of polymer present in the fabric.

[0082] In FIG. 3 the metal cords forming the warp are widely spaced andare crisscrossed by a bundle or a group 36 of polymer filaments 34. Thepolymer filaments could thereby be interlaced.

[0083]FIG. 4 shows a woven structure 40 whereby the warp and the weftfilaments are a combination of metal cords and polymer filaments. Thewarp and the weft filaments comprise in turn a steel filament 42 and apolymer filament 44.

[0084] The number of metal cords and the number of polymer filaments,either in the warp or in the weft could thereby be varied.

[0085]FIG. 5 illustrates a knitted structure 50. Polymer filaments 52and cords 54 are knitted together.

[0086] In order to increase the volume of the thermoplastic material,thermoplastic material can be applied on the fabric.

[0087]FIG. 6 shows a steel cord 64 on which a coating of a thermoplasticmaterial 66 is applied.

[0088]FIG. 7 is an embodiment of the second group of fabrics. Both thewarp and the weft of the woven fabric 70 comprise coextruded steel cords72.

[0089]FIG. 8 shows a strip 80, comprising a number of elongated metalcords 82, embedded in a matrix of a thermoplastic material 84.

[0090]FIG. 9 is an illustration of embodiments of the third group offabrics. It shows a woven structure 90 comprising coextruded steelstrips 92.

[0091] The adhesion between the metal cord and the thermoplasticmaterial could be determined by performing a pull-out test.

[0092] In this test, the force needed to pull a metal cord, which is atone end embedded in a matrix of thermoplastic material over a short andwell-controlled length, out of the matrix is determined. The length ofthe metal cord embedded in the thermoplastic material was 12.7 mm.

[0093] Two types of steel cords, more particularly of the type 7×3×0.15and 2×0.3, are embedded in different matrices. The thermoplasticmaterials considered in the test are polyamide (PA), polycarbonate (PC),polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP)and thermoplastic polyurethane.

[0094] For the cord of the type 7×3×0.15 embedded in a matrix of PA, PCor PET, a good adhesion was obtained. The pull-out force equals thetensile strength of the 7×3×0.15 cord. 100% of the steel cords werebroken while pulled out.

[0095] If the cord is coated with brass or zinc, the adhesion to thethermoplastic material can further be improved.

[0096] For the cord of the type 2×0.3, the best adhesion was obtainedwith PET as matrix.

[0097] If the results of the two tested types of steel cords arecompared, the cord of the type 7×3×0.15 gives the best adhesion.

[0098] It seems that a cord with a great specific surface gives a betteranchoring in the matrix and as a consequence such a cord gives a goodadhesion.

1. A fabric comprising elongated metal elements and thermoplasticmaterial, said thermoplastic material being present in a volume of atleast 40% of the total volume of said fabric, characterised in that atleast part of the elongated metal elements are metal cords.
 2. A fabricaccording to claim 1, whereby said fabric is a woven, knitted or braidedstructure.
 3. A fabric according to claim 1 or 2, whereby said metalcords are steel cords.
 4. A fabric according to any one of claims 1 to3, whereby said thermoplastic material is selected from the groupconsisting of polyethylene (PE), polypropylene (PP), polystyrene (PS),polyethylene terephthalate (PET), polyethylene napthalate (PEN),polybuteen terephthalate (PBT) polyvinylchloride (PVC), polyester,polyamide (PA), polyimide (PI), polycarbonate (PC), styrene acrilonitryl(SAN), acrylonitril-butadiene-styrene (ABS), thermoplastic polyurethane(TPU), thermoplastic polyolefins (TPO), thermoplastic copolyetherestersor copolymers of these polymers.
 5. A fabric according to any one ofclaims 1 to 4, whereby said fabric comprises metal cords and polymerfilaments, said polymer filaments being made of a thermoplasticmaterial.
 6. A fabric according to claim 5, whereby said fabric is awoven structure, comprising a warp and a weft, at least one of the warpor the weft comprising said polymer filaments.
 7. A fabric according toany one of claims 1 to 4, whereby said fabric comprises metal cordscoated with a thermoplastic material.
 8. A fabric according to claim 7,whereby said fabric is a woven structure, comprising a warp and a weft,at least one of the warp or the weft comprising metal cords coated witha thermoplastic material.
 9. A fabric according to any one of claims 1to 4, whereby said fabric comprises strips, said strips comprising atleast two elongated metal cords embedded in a matrix of a thermoplasticmaterial.
 10. A fabric according to claim 9, whereby said fabric is awoven structure comprising a warp and a weft, at least one of the warpor the weft comprising said strips.
 11. A fabric according to any one ofclaims 1 to 10, whereby a thermoplastic material is applied on thefabric.
 12. The use of a fabric according to any one of claims 1 to 11for the manufacturing of a reinforced article.
 13. A method ofmanufacturing a reinforced article comprising the steps of providing afabric according to any one of claims 1 to 11 or providing a layeredstructure comprising at least two layers, each layer comprising a fabricaccording to any one of claims 1 to 11; applying heat and/or pressure tosaid fabric or to said layered structure to form said reinforcedarticle.
 14. A method of manufacturing a reinforced article comprisingthe steps of providing a fabric according to any one of claims 1 to 11or providing a layered structure comprising at least two layers, eachlayer comprising a fabric according to any one of claims 1 to 11;applying heat to said fabric or to said layered structure to soften saidthermoplastic material; applying a force to the heated fabric to obtaina reinforced shaped article.
 15. A reinforced article obtainable byapplying heat and/or pressure to a fabric according to any one of claim1 to 11 or to a layered structure comprising a number of fabricsaccording to any one of claim 1 to 11.